Calculates the power spectrum of a signal that is unevenly spaced in time.


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Inputs/Outputs

  • c1ddbl.png XTime —

    XTime is the discrete- and unevenly-spaced times.

  • c1ddbl.png X —

    X represents the data material at times XTime.

    There is a one-to-one relation between XTime and X.

  • i1ddbl.png Power Spectrum FFT {X} Frequency —

    Power Spectrum FFT {X} Frequency are the frequency points at which the power spectrum is calculated.

  • i1ddbl.png Power Spectrum FFT {X} —

    Power Spectrum FFT {X} is the power spectrum, in the sense of the Lomb normalized periodogram.

  • ii32.png error —

    error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

    • The algorithm used is based on the Lomb normalized periodogram. Let the data Xk be given at the time points tk. In other words,

    X = {x0, x1, …, xn – 1}

    and

    XTime = {t0, t1, …, tn – 1}.

    Furthermore,

    and

    .

    Then the Lomb normalized periodogram is defined as

    ,

    with

    The following diagram shows the Fourier transform of length 256 of a signal that has been sampled at unequal intervals of time. The signal is a combination of sine waves of frequencies 20, 40, 60, and 80 Hz. The duration of the signal is 1 sec. The sampling frequency was chosen as 256 Hz, giving the frequency resolution of 1 Hz.

    Examples

    Refer to the following example files included with LabVIEW.

    • labview\examples\Signal Processing\Transforms\Generalized Fourier Spectrum.vi
    • labview\examples\Signal Processing\Transforms\FFT and Power Spectrum Units.vi